K. R. Bestgen, K. A. Zelasko, and G. C. White. Monitoring ...

are spawning in the tributary itself. It is noteworthy that sampling in the San Rafael River
confluence area produced some of the largest razorback sucker larvae captured from 1993–1999.
Better information on distribution and abundance of larvae may assist with understanding
reasons for the occasional larger age-0 or juvenile-sized razorback suckers found in that reach
(Gutermuth et al. 1994, three 100+ mm fish captured in 2008, P. Badame pers. comm., Utah
Division of Wildlife Resources).
Colorado River Basin.—Adult razorback suckers have also been heavily stocked in the
Gunnison and Colorado rivers, Utah and Colorado, beginning in 1994 (Burdick 2003;
Osmundson and Seal 2009; Zelasko et al. 2011) but reproductive success has apparently been
limited. Seine sampling from 2002–2007 in the lower 57 miles of the Gunnison River detected
presence of nine positively identified razorback sucker larvae and 33 larvae identified as
“razorback sucker?” (larvae whose taxonomic identity is slightly uncertain) among over 66,000
fishes examined from 1,032 samples (Osmundson and Seal 2009). Razorback sucker larvae
were captured from just downstream of Delta, Colorado, downstream to near the confluence with
the Colorado River.
Sampling in the Colorado River from 2004–2007 from upstream near Government
Highline Canal downstream to Westwater, Utah, yielded 23 positively identified razorback
sucker larvae and 1 larva identified as “razorback sucker?” among 26,000 fishes examined from
670 samples. Razorback sucker larvae were widespread in samples in spite of low abundance
(see Osmundson and Seal 2009 for details). Abundance of adult fish may be low; an estimated
1,066 adult razorback suckers > 400 mm TL inhabited the Colorado River in 2005 in spite of
stocking nearly 80,000 larger juvenile and adult fish through 2005 (Osmundson and Seal 2009,
Zelasko et al. 2009; 2011). Ripe females, which may indicate locations of spawning adults, were
distributed over a broad area from Fruita, Colorado, downstream to Moab, Utah. Low
abundance of adults combined with widespread distribution may explain the widespread pattern
of razorback sucker larvae.
As was suggested by Ryden et al. (2011, Colorado-Gunnison River sampling scope of
work, Recovery Program project 163), we support continued sampling of razorback sucker
larvae in the Gunnison and Colorado rivers. Sampling needs to be widespread based on broad
distribution of running ripe females and larvae detected in an earlier study (Osmundson and Seal
2009) and should include light traps in appropriate locations including gravel pit ponds (e.g.
Maggio Pond). Since samples and large numbers of all sucker larvae are easy to obtain but
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